Buttock cleavage, also known as butt crack, is the little line you can sometimes see between a person's butt cheeks. This happens when their pants, shorts, or underwear are too low and the fabric doesn't cover their bum completely. It's kind of like when you sit down and your shirt rides up a little bit, showing your tummy. Except in this case, it's your bum that's exposed. Some people like to show off their buttock cleavage by wearing low-cut pants or shorts, while others prefer more coverage. It's important to remember that everyone's body is different and it's okay to dress however you feel comfortable.